This application is the national phase of international application PCT/GB94/01224 filed June 6, 1994 which designated the U.S.
This invention relates to the cathodic protection of reinforced concrete.
The application of cathodic protection to steel reinforcement in concrete is an accepted method of providing corrosion protection for the metal, particularly where chloride ions are present at significant concentrations in the concrete.
Cathodic protection involves the formation of a circuit with the reinforcement acting as a cathode, electrically connected to an anode, with the circuit being completed by pore solution in the concrete and an electrolyte contacting the anode. When a potential difference exists corrosion of the cathode is prevented or reduced.
It is known to create a potential difference between an anode and a cathode both by means of impressed current cathodic protection which involves the use of a non-sacrificial anode and an applied electric current using an external DC power supply and by means of a galvanic cell in which the potential arises as a result of the different materials forming a sacrificial anode and a cathode.
Where a galvanic cell is used it is important that the electrolyte contacting the anode is such that sustained active corrosion of the anode can occur. If suitable conditions are not maintained then the cathodic protection will become inefficient.
Furthermore, the electrolyte must be such that its contact with the surrounding concrete does not result in the degradation of the concrete. Of particular significance in this context is the susceptibility of some aggregates, present in concrete, to alkali-silica or ine the aggregate reactions. These reactions can cause swelling and consequential cracking of concrete.